It is frequently desired to limit the accessibility of a calculator keyboard to a selected group of keys, e.g. for avoiding errors in carrying out a special program or for preventing unauthorized personnel from altering or erasing instructions and data already fed into its memory in a preprogramming operation.
Furthermore, in a calculator whose keys are not fixedly wired to its logical circuitry but are selectively connectable thereto by the insertion of a stored-program cassette, a need exists for variably labeling the operative keys in conformity with the chosen program.